1. Field of the Invention
The present invention relates to a highly reliable rechargeable lithium battery and a process for the production thereof. More particularly, the present invention relates to a highly reliable rechargeable lithium battery provided with an improved cathode constituted by a specific cathode active material and which is high in charge-and-discharge efficiency and also in discharge capacity, and it also relates to a process for the production of said rechargeable lithium battery.
2. Related Background Art
In recent years, global warming from the so-called greenhouse effect has been predicted due to increased levels of atmospheric CO2. To prevent this warming phenomenon from further developing, there is a tendency to prohibit the (construction of new steam-power generation plants which exhaust a large quantity of CO2.
Under these circumstances, proposals have been made to institute load leveling in order to effectively utilize power. Load leveling involves the installation of rechargeable batteries at general locations to store surplus power unused in the night, known as dump power. The power thus stored is available in the day time when the power demand is increased, thereby leveling the load requirements in terms of power generation.
Separately, there is an increased societal demand for developing a high performance rechargeable battery with a high energy density for an electric vehicle which would not exhaust air polluting substances. There is further increased societal demand for developing a miniature, lightweight, high performance rechargeable battery usable as a power source for portable instruments such as small personal computers, word processors, video cameras, and pocket telephones.
In order to attain such a miniature and light weight rechargeable battery, the use of a lithium-graphite intercalation compound as an anode active material has been proposed (see, Journal of the Electrochemical Society, 117, 222 (1970)).
Since then, public attention has focused on a rocking chair type lithium ion battery. Various studies have been made in order to develop such a rocking chair type lithium ion battery. The rocking chair type lithium ion battery is typically configured such that a carbon such as graphite is used as an anode active material and an intercalation compound intercalated with lithium ion is used as a cathode active material, and lithium ion is intercalated at an intercalation of the six-membered network plane provided by carbon atoms and thereby stored in the battery reaction upon operating charging. Presently, there are several known rocking chair type lithium ion batteries having such configuration which are suitable for practical use. In these lithium ion rechargeable batteries, the carbon serving as a host of intercalating the lithium ion is used as the anode active material to prevent the growth of a lithium dendrite, thereby prolonging the charging and discharging cycle life.
However, based on the configuration of the above lithium ion battery, there cannot be attained a desirable rechargeable lithium battery having an electric capacity and energy density similar to those of a primary battery in which a lithium metal is used as the anode active material.
In order to solve this problem, research and development studies are being made in order to develop a desirable carbon material capable of attaining an improved electric capacity for use as a constituent of the anode in the lithium ion battery.
Separately, in order to realize the production of a rechargeable battery with a high energy density, it is essential to develop not only such an anode material but also an effective cathode material capable of attaining an improved electric capacity. Presently, a lithium-transition metal oxide as an intercalation compound intercalated with lithium ion is principally used as the cathode active material. However, the use of this lithium-transition metal oxide can attain only 40 to 60% of the theoretical discharge capacity. Therefore, in the case of a rechargeable lithium battery including a lithium ion battery in which lithium ion is utilized as a guest in the charging and discharging reactions, there is an increased demand for attaining an improvement in the charging and discharging cycle life and also an improvement in the cathode so that it provides a high electric capacity.
An object of the present invention is to provide a highly reliable rechargeable lithium battery using an electrochemical intercalation reaction of lithium ion (that is, electrochemical insertion reaction of lithium ion) and an electrochemical deintercalation reaction of lithium ion (that is, electrochemical release reaction of lithium ion) (this rechargeable lithium battery will be hereinafter simply referred to as rechargeable lithium battery), which is provided with an improved cathode constituted by a specific powdery cathode active material having a primary particle size of 0.5 xcexcm or less and a large specific surface area, and which has a large electric capacity with a high energy density and a high charge-and-discharge efficiency, and is long enough in cycle life (charging and discharging cycle life).
Another object of the present invention is to provide a highly reliable rechargeable lithium battery having a large electric capacity with a high energy density and a high charge-and-discharge efficiency and which is long enough in cycle life, comprising at least a cathode, a separator, an anode, and an electrolyte or electrolyte solution integrated in a battery housing, characterized in that said cathode is constituted by a specific powdery cathode active material having a primary particle size of 0.5 xcexcm or less and a large specific surface area.
A further object of the present invention is to provide a process for the production of aforesaid rechargeable lithium battery.
Particularly, the present invention provides a process for the production of a highly reliable rechargeable lithium battery having a large electric capacity with a high energy density and a high charge-and-discharge efficiency and which is long enough in cycle life, comprising at least a cathode having a specific cathode active material, a separator, an anode, and an electrolyte or electrolyte solution integrated in a battery housing, characterized in that said process includes a step of preparing said cathode active material constituting said cathode, comprising mixing a salt of a transition metal in an aqueous solution containing at least a water-soluble polymer and dissolving said transition metal salt in said aqueous solution to obtain a product, and baking said product to form a powdery cathode active material.
Further, the present invention provides a process for the production of a highly reliable rechargeable lithium battery having a large electric capacity with a high energy density and a high charge-and-discharge efficiency and which is long enough in cycle life, comprising at least a cathode having a specific cathode active material, a separator, an anode, and an electrolyte or electrolyte solution integrated in a battery housing, characterized in that said process includes a step of preparing said cathode active material constituting said cathode, comprising mixing a salt of a transition metal in a monomer capable of forming at least a water-soluble polymer, polymerizing said monomer to obtain a polymerized product, and baking said polymerized product to form a powdery porous cathode active material.